Castable explosive containing tnt and a reaction product of a diisocyanate and 1,4-butyleneoxide polyglycol



United States Patent 3,447 980 CASTABLE EXPLOSIVE CONTAINING TNT AND A REACTION PRODUCT OF A DIISOCYANATE AND 1,4-BUTYLENEOXIDE POLYGLYCOL H. William Voigt, Jr., Stanhope, N.J., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Jan. 20, 1967, Ser. No. 610,697 Int. Cl. C06b 9/04 US. Cl. 149-19 Claims ABSTRACT OF THE DISCLOSURE A polyurethane modified castable high explosive, such as TNT or Petrin Acrylate, whose solidified cast is essentially free of voids, cavities, or exuding oils.

This invention relates to a castable high explosive of the type based on 2,4,6-trinitrotoluene or some analogous melt medium such as pentaerythritol acrylate trinitrate.

As is well known, castable high explosives are not only required in the manufacture of large caliber shells but are also preferred in the manufacture of other type shells due to simplicity in handling, safety achieved in loading, and overall cost in manufacture.

In the past, characteristics such as exudation, cavitation, brittleness, and irreversible expansion were noted in the preparation of a castable high explosive such as 2,4,6 trinitrotoluene. In the case of exudation, the low melting oils usually appear when the cast is stored around 71 C. but may appear even at room temperature. This leads to cavitation and independent spinning of the cast when the shell is fired from a rifled barrel. Also, the physical nature of the cast is usually brittle, particularly at the low temperatures required of military use, and cracking occurs when the cast is cycled from differing zones of temperature. The latter condition ultimately affects the impact sensitivity of the cast. Further, the coefficient of thermal expansion of this type castable explosive is high and irreversible expansion of the cast occurs when heated. This facilitates the formation of voids which also adversely'infiuences the impact sensitivity of the final cast.

The subject invention essentially eliminates the aforesaid disadvantages which are inherent in the manufacture of cast explosives by treating such explosives during manufacture with a mild, two-component, liquid polyurethaneproducing system.

It is therefore an object of this invention to provide a polyurethane modified castable high explosive whose solidified cast is essentially free of voids, cavities, or exuding oils.

Another object is to provide an improved high explosive cast which, as a result of its composition, exhibits a higher degree of impact strength and a lesser degree of brittleness 55 when compared to similar explosives of the art.

3,447,980 Patented June 3, 1969 Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description.

It has been found that a selected polyurethane elastomeric system may be so-melted as homogeneous liquids with 2,4,6-trinitrotoluene to achieve the advantages described above. The polyurethane-producing system consists of a liquid polymeric diisocyanate prepolymer, such as the reaction product of 2,4-tolylene diisocyanate and 1,4butylene oxide polyglycol, accompanied by a suitable curing agent such as a liquid polyol or melta'ble hydrogenated castor oil. In theory, it is possible that strong hydrogen bonding of the -NH groups of the urethane system occurs with the available oxygen of the trinitrololuene or pentaerythritol acrylate trinitrate molecule, resulting in the advantages described above. The aforementioned polyurethane-producing system is selected from many other similar systems because it is essentially non-reactive with 2,4,6-trinitrotoluene as determined by the standard 120 C. vacuum stability test of the final cast product.

The polyurethane producing system should be present together in an amount between about 4 to 45 percent by weight of the total composition including the high explosive component. If the high explosive is present in an amount below percent, there would be a major decrease in explosive power and the entire composition, under normal initiation procedures, would merely defiagrate rather than explode. However, if the explosive is present in an amount greater than about percent, the mechanical strength of the composition would be proportionately decreased as the polyurethane content is reduced.

The curing agent component, i.e. hydrogenated castor oil, for eifective activity should be present in a ratio of about 1 part curing agent to 2 parts of the prepolymer component of the polyurethane system. Therefore, in the range above, the curing agent would be present in an amount between 1.7 to 15 percent by weight of weight of the total composition. The polyurethane producing system would then represent about 3.3 to 30 percent by weight of such composition.

During preparation, the liquid trinitrotoluene and the liquid polyurethane producing system may form two separate layers. A mild agitation of these components by means of a paddle will bring them into a blended mixture. However, to aid this process, a melt compatibilizer such as poly-alpha-methylstyrene may be added which will facilitate the miscibility of the admixture. This type material represents a low molecular weight, liquid, polymeric material and results have shown, it only need be present in an amount up to that of the curing agent in the admixture to facilitate miscibility of the components.

The data set forth in Table I below will illustrate the etfectiveness of this invention.

TABLE I Composition Control A B C Percent by weight:

TNT Urethane prepolymer Curing Agent.

Compatibilizer Vacuum Stability: 5 at Crystallinity on solidification mls.

0-2mls 0-2 Inls Amorphous or micro- Amorphous or micro- Amorphous or microcrystalline. crystalline. crystalline. Light Yellow Light Yellow Light Yellow. 5.5 7 0 9,

Firm. None.

100. Non-Brittle.

As may be seen from the above cited data, the explosive composition incorporating the polyurethane producing system is highly stable, free of cracks and evidence of exudation, and substantially less brittle than the explosive composition which served as a control. Further, the treated explosive is firmly bonded to the containers While the control is only negligibly bonded and, as heretofore stated, the latter actions leads to independent spinning of the cast when fired.

A castable high explosive which is equivalent to TNT in this composition is pentaerythritol acrylate trinitrate also known as petrin acrylate. The latter explosive also exhibits exudation prior to treatment due to the incorporation of low melting plasticizers. Further, the TNT or petrin acrylate in the composition may be replaced with up to 80 percent by weight of cyclotrimethylene trinitramine, also known as RDX, or cyclotetramethylene tetranitramine which is conventionally known as HMX. Such replacement will tend to upgrade the composition leading to a greater explosive power, a less likelihood that the TNT will melt out when stored at a high temperature or that the final cast will possess cracks.

The following examples will illustrate how efiective the replacement may be.

'4 tages with results similar to that obtained in Table H may be achieved, if the polyurethane modified TNT is replaced with up to 80% HMX.

Obviously, many modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as described.

I claim:

1. A composition of a high explosive cast which is free of voids, cavitations, and exudation of oils up to a temperature of 71 C. consisting of (a) 55 to 95 percent by weight of 2,4,6-trinitrotoluene,

and

(b) 5 to 45 percent by weight of the reaction product of 2,4-tolylene diisocyanate and 1,4-butylene oxide polyglycol.

2. The composition of claim 1 wherein cyclotrimethylene trinitramine is substituted for up to 80 percent of the base weight of TNT in said composition.

3. The composition of claim 1 wherein cyclotetramethylene tetranitramine is substituted for up to 80 percent of the base weight of TNT in said composition.

4. The composition of claim 1 wherein said reaction TABLE II Composition Control A B C 18. 4 36. 8 55. 2 73. 6 55. 2 36. 8 Prepolymer 4 4 4 Polyol Curing Agent... 2 2 2 Melt Compatibilizer 2 2 2 Characterization: Rate of deto tor, meters per second. 6, 640 6, 800 7, 300 7, 600 7, 900 7, 900 Cast density, g./cc 1. 56 1. 60 1. 03 .65 1. 67 1. 72 200 g. Bomb Brisance, sand crushed, g.: Detonator ehg. wt., 0.2 gm. azide, 0.1 gm. tetryl 48. 0 50 51 52 54. 6 54. 6 hr. Vacuum stability, 120 C., 5 gms., ml. gas.-- 0.20 1.0 1.0 1.0 0.7 0.3 Explosion temp., 5 secs. C. (to decomposition) 475 400 300 300 275 280 Impact Sensitivity, 2 kg. wt. ht. in inches (.017

mg. in confined cup) 14 17 17 17 17 14 Hardness, Shore D 1 45 K 45 Brittleness, falling ball, V lb. steel ball, approx.

height to cause fracture, inches... 2 8 8 8 8 2 Remarks: Melt Pouring temp., C 85 85 85 85 85 Curing temperature Physical properties Exeuding in shell, 71 C Yes None None None None Yes Temperature cycling, 40 C. to +71 C Suspension or Settling out of RDX or HMX filler in melt phase (0 Temperature of melting-out of TNT, C 80 105 80 1 Brittle. I N/a. 3 Room temperature 71 C. 4 Non-brittle. Elastomeric. Cracks develop. 7 No cracks. 8 Suspension. 9 Settling out.

In Table II above, 20 to 80% of the polyurethane modilied TNT is replaced with RDX. As indicated, the rate of detonation, cast density, hardness and brisance are increased as the amount of RDX is increased in the composition. Also, the vacuum stability is negligibly afiected while the impact sensitivity is only slightly increased. Further, the physical properties of the case are such that the cast may be characterized as non-brittle while the control, which is unmodified, is quite brittle. In any case, the unmodified casts exude oils While there is no evidence of this type activity in the modified samples. Thus, the modified samples are not liable to cavitation and independent spinning of the cast when fired. Further, no cracks are evident in the modified samples when cycled from -40 to 71 C. which means that the impact sensitivity of the cast will not be afiected. As is apparent from the above, the replacement of TNT with RDX is accompanied by many advantages. However, similar advanproduct is accompanied by a polyol curing agent selected from the group consisting of castor oil and hydrogenated castor oil.

5. The composition of claim 4 wherein said reaction product is accompanied by poly-methyl styrene.

References Cited UNITED STATES PATENTS 3,049,454 8/ 1962 Stark 149-92 3,141,294 7/ 1964 Lawrence et a1 14919 3,238,245 3/ 1966 Reedy 149-93 X 3,309,247 3/1967 Bluhn 149-19 X 3,350,245 10/1967 Dickinson 14919 BENJAMIN R. PADGETT, Primary Examiner.

US. Cl. X.R. 

